It is important for a mobile network to govern the current location of a mobile station, in order to provide prompt service for the mobile station. In this way, the mobile network can rapidly determine the location of the mobile station, set up the connection and transfer information to/from the mobile station, when there is information such as call or short message to be sent to the mobile station or when the mobile station sends out information. A mobile station may be moving while it is engaged in a communication or in an idle state. To ensure the continuity of an already initiated connection, the mobile station is handed over between the access points. When a mobile station is not engaged in a communication, the network must be able to determine its current cell in order to setup and route an incoming connection.
Location management in current mobile network such as GSM is carried out by two basic operations: paging and location updating. At the radio link level, paging refers to that procedure whereby the network searches for the exact cell through which a mobile station can be reached. This is done by sending out polling signals through all the candidate base stations. If paging is successful, the mobile station will send a paging response to the base station through which the mobile terminated connection can be set up. Location updating refers to that procedure whereby the mobile updates the stored current location and informs the network about its current location when the current location of the mobile station is not consistence with that stored inside the mobile station, so the current location of the mobile station can be managed by the mobile network and an exhaustive search through all possible base stations can be avoided.
FIG. 1 shows the paging and the location updating procedure implemented in a GSM network. Similar approaches are also employed in other mobile networks. With the conventional location management strategy, the network coverage area is divided into smaller cell cluster called Location Areas (LA). A location area is the granularity at which the network keeps track of the locations of the mobile stations, i.e., a location area is that group of cells in which the mobile station must be located. When a mobile station moves from one location area to another, a location updating procedure is triggered and the mobile station informs the network about this change of location area.
To enable the mobile station to detect a change of location area, the base stations periodically broadcast the identifiers of the location area they belong to; the identifier is called the location area identifier (LAI). On the other side, the mobile station ‘listens’ to the LAI currently being broadcasted and compares it to a recorded LAI (the LAI where it was last located). If the two LAIs are identical, the mobile station does not do any work. However, if the two lAIs are different, the mobile station interprets this as a change of location area, a location updating procedure is triggered and the old LAI is replaced with the new one. At the same time, the mobile station notifies the mobile network the change of its LAI. The mobile network processes the updating procedure on its side in response to receiving the notification, so as to promptly manage the current location of the mobile station.
In the conventional location updating management mechanism, a base station continuously broadcasts the LAI of the location area it belongs to, while a mobile station continuously ‘listens’ to the broadcasted LAI, and compares it to the registered one. If the two lAIs are different, the mobile station notifies the mobile network the change of its LAI. The mobile network processes the updating procedure on its side, in response to receiving the notification. Then the problem is raised that the overhead of the network increases very much and the network resource is wasted. Furthermore, the power of the mobile station is consumed very quickly because of continuously transmitting signals from the mobile station to the mobile network.
In practice, the activities of many users of mobile stations can be modeled. For instance, quite a number of office workers go to the offices in the morning, stay there for 9 hours, and go back to home. Thus, the location updating process can be done at specific switching points, such as at the points when the user arrives at the offices and when he/she arrives at home, if the mobile network knows about the mobility pattern of a mobile user. In this way, the continuous information exchange between a mobile station and a mobile network is avoided. The information exchanged between the mobile station and the mobile network is reduced then, the location updating process in the system and the process in the mobile station are simplified.
Research already shows that using mobility model of individual user can increase the efficacy of location management. But all proposed methods store and use the mobility model on the mobile network side with little participation of mobile stations, except for them to know location area and compare old and new location areas. Amount of other work is done on the mobile network side.
The mobile station is becoming more powerful with the development of the technique of the embedded microprocessor and storage. Many processes done in the mobile network, in turn, can be done in the mobile station. In addition, a mobile station can locate itself through GPS (Global Positioning System), the LAI received from the mobile network or their combination.